It is highly desirable to secure the cover of a personal computer in order to protect information stored in the computer and to prevent unauthorised access to or removal of the components within the case.
One known lock system used for instance in the HP Vectra series of computers is a mechanism similar to a conventional key operated lock, actuated by a key in the rear of the machine. Two people are enabled to unlock the cover: the key owner and the system manager. The system manager can open all machines that he is in charge of using a programmable master key. Other examples of key operated locks can be found described in U.S. Pat. No. 5,548,981 and U.S. Pat. No. 5,598,323.
One of the main advantages of using key operated locks is that the cover can be removed even if there is no power on. However, if a technician is required to open the computer to repair or replace a component, then that person must be physically in possession of one of the keys. It is not with this system possible to provide for software control of the lock to enable desirable functionality such as remote locking and unlocking of the cover or password controlled access.
Such features are particularly desirable for customers that own and manage very many PCs, and therefore that need to manage access to hardware more easily. If hardware changes are desired in many machines at the same time, the system manager can access systems without having to locate keys and can unlock machines over a computer network, using appropriate hardware management software tools like ones included in the HP Toptools package, available from Hewlett-Packard Company.
In order to allow remote locking and unlocking of computer covers, electronically controlled cover lock mechanisms have been used. For example the Compaq Deskpro 4000 and 6000 models employ an electromechanical lock that use a bistable solenoid.
A bistable lock is needed because safety specifications require the machine to be switched off for the removal of the cover. In consequence, the unlocked position of the soft lock has to be mechanically stable. Since the need for security requires that the lock prevent the removal of the cover even if the machine is not supplied with power, the lock position has also to be mechanically stable.
A suitable bistable solenoid for use in such locks is the MSA model L-09432 that is available from MAGNET-SCHULTZ OF AMERICA. This solenoid is electronically connected to the computer motherboard by 3 wires (-12V, 0, 12V). The locking and unlocking operation is performed by powering the solenoid during one second.
Whilst this solution is generally satisfactory, it is relatively expensive and does present certain drawbacks. For instance, use of a solenoid creates a certain amount of electromagnetic radiation. Since the electromagnetic emissions from computers are subject to strict controls, extra shielding or special design of the case may be required to reduce the radiation coming from the solenoid. In addition, the solenoid coil itself is inevitably somewhat bulky and adds to the weight of the computer.
This invention is directed to mitigating the drawbacks of the prior art.